Kaffe JVM Java Virtual Machine. Works on many platforms and includes Just-In-Time (JIT) support for most of them. PersonalJava 1.1 compliant (but does not fully support the Java 2 Platform). [Open Source, GPL]

Open Runtime Platform Open source research infrastructure for dynamic compiling and memory management; supports programs compiled to bytecode and linked with GNU Classpath libraries. [SourceForge, Open Source, Intel]

shuJIT JIT plugin for the Sun JVM, for Linux and FreeBSD on x86 processors. Includes support for a transparent distributed object system, MetaVM. [Open Source, GPL]